Hi,

It’s possible your profile still contains the data, but Firefox is using a new or wrong profile, or the database files couldn’t be read. Here's what to check and do:

1. Verify you're using the correct profile Type about:profiles in the address bar. If you see multiple profiles, try launching an older one using "Launch profile in new browser" to check whether your bookmarks and history return. If one works, set it as the default.

2. Restore bookmarks from backup Firefox automatically saves backups in your profile under the bookmarkbackups folder. Open the Library window → Import and Backup → Restore, and choose a recent backup. If restore fails, you can manually extract the .jsonlz4 files using external tools.

3. Rebuild your places database If you see the error “The bookmarks and history system will not be functional,” close Firefox, then delete or rename places.sqlite and favicons.sqlite in your profile folder. Restart Firefox—this will create fresh databases. After that, restore bookmarks from backup if needed.

4. Check for file locks or permissions issues Make sure files like places.sqlite aren't locked by antivirus or backup software, and that file permissions allow Firefox to read and write them.

5. Avoid profile downgrades If you temporarily downgraded to 140, Firefox may have created a new profile. When you go back to 141, it might again create or switch profiles automatically. Always manage profiles via about:profiles.

Response to item 1: When I install a new version, I install it over the currently installed version - which is in D:\Firefox and the profile is in M:\Firefox. In the past Firefox has used the existing profile.

I'm currently working with the Bugzilla resource to diagnose this problem, but according to my post there, it appears this is also a problem with some other users.